class Solution {
public:
    void duplicateZeros(vector<int>& arr) {
        int cur = 0;
        int dest = -1;
        int n = arr.size();
        while (cur < n)
        {
            if (arr[cur] == 0)
                dest += 2;
            else
                dest++;
            if (dest >= n - 1)
            {
                break;
            }
            cur++;
        }

        if (dest == n)
        {
            arr[dest - 1] = 0;
            cur--;
            dest -= 2;
        }

        while (cur >= 0)
        {
            if (arr[cur] != 0)
            {
                arr[dest] = arr[cur];
                dest--;
            }
            else
            {
                arr[dest--] = 0;
                arr[dest--] = 0;
            }
            cur--;
        }

    }
};